Bokeh (from the Japanese boke ぼけ, "blur") is a photographic term describing the subjective aesthetic qualities of out-of-focus areas in an image produced by a camera lens.--Wikipedia article (footnote omitted)
Bokeh is much more important when your depth of field is shallow. It's something that is essentially beyond your control, as it's determined entirely by the lens you're using (both flaws in the glass and the shape of the aperture). It's also very subjective, but most consider good bokeh to be very fuzzy, soft blur, while bad bokeh will be sharper shapes.
There's no real way to quantify it, so it's hard to evaluate. But it seems to be gaining in importance in the US, while it's been important in Japan for many years. Some day you may expect to hear about bokeh on a regular basis when asking for critiques of your photos.